We have a mud room, which is a small addition to the front of our property - added probably 10 - 15 years ago. It houses our coats and shoes and bags.

For the last two days it has smelled really moudly in there - I went through everything in there yesterday, doing the sniff test and nothing smells mouldy, just the room itself.

My plan tonight is to remove everything and see if the smell remains. Any ideas what it could be? Could it be water getting into the roof/wall space and making the insulation mouldy?

What's on the floor? Mats, rugs, or just bare floor? If mats or the like, turn them over, could be mold on the bottom.

Otherwise, you could be right, possibly in the insulation

Edited to add - are there gutters/eavestroughs on the mudroom? If the gutters are full of moldy, decaying leaves, the smell might be getting in.

The floor is just a tiled floor - no mats of anything.

No gutters around that part of the house either - I am sure it is the insulation but him indoors says not...let's see who is right!

If the vapor barrier was not sealed properly when the addition was done it can also cause damp and mold problems behind the wallboard. It will also take some time for this to manifest itself.

I think it may have something to do with the new roof that was put on after last years nightmare...may have to send hubs up into the loft to have a dig around.

If so, have him check how many vents there are at the bottom of the roof, where it meets the vertical wall. There should be Styrofoam vents to allow air circulation in the attic or loft to the outside.
Is there an internal fan, in a bathroom for instance, that is vented into the attic ?
What is under the mud room ? Basement or concrete ?

Looks like Google Ads have solved the problem:

Was the previous owner a serial killer ? Tiled floor and all that.

Its funny to watch the people try and dance to this.

There is one vent into/out of the mud room. This section does not have the styrofoam vents though the rest of the house does - it just has one large square vent at the front.

Under the mud room is concrete.

Uh-oh! We had a mouldy smell, turned out half the exterior walls were rotted through from poorly installed windows/doors and deck causing many leaks, plus the stud walls were about eight inches below grade!

Some options I can suggest are:

1) Pulling off some dry wall (the expensive & messy) and having a gander.

2) Get a moisture sensor and run it around the walls/ceiling of the offending room.

3) Get a home inspector in to do it for you (also expensive, but a good one "should" have the right equipment to trace the problem).

Whatever you do - don't ignore it.
Good luck.

When we had the flood last year, the contractors ripped out all the drywall and insulation - except in this room - absolutely no idea why they left it - a brown spot appeared on the ceiling which I pointed out - they cut a hole and waved an arm into the hole and that was that.

They were paid to do the work in there but never did - I can only assume it is from the insulation not being removed - the rest of the attic space now has blown in insulation - the space above this room still has the old insulation that got soaking wet. Needless to say I am on to the insurance company today to see what they will do to help out.

Good idea...

Also, I noticed that our crappy tire flyer has moisture sensors much reduced (now $70 IIRC).. yours may have too.

Given the flooding and the brown spot, and the lack of remedial work in the mud room after the flood, it doesnt sound like the smell is going to go away on its own Im afraid....

Yup I tend to agree. The insurance guy is currently ignorning my calls - I may have to step it up a notch to voicemails left every 10 mins..lol

Well that worked - the Contractors who I despise will be out this afternoon with a machine (that probably means a torch) to see what is causing the stinky stench.